State Key Laboratory for Crop Genetics and Germplasm Enhancement, Jiangsu Nanjing National Field Scientific Observation and Research Station for Rice Germplasm, Nanjing Agricultural University, Nanjing, 210095, China.
National Key Facility for Crop Gene Resources and Genetic Improvement, Institute of Crop Science, Chinese Academy of Agricultural Sciences, Beijing, 100081, China.
J Integr Plant Biol. 2022 Oct;64(10):1883-1900. doi: 10.1111/jipb.13333. Epub 2022 Sep 14.
Grain size is a key agronomic trait that determines the yield in plants. Regulation of grain size by brassinosteroids (BRs) in rice has been widely reported. However, the relationship between the BR signaling pathway and grain size still requires further study. Here, we isolated a rice mutant, named small grain2 (sg2), which displayed smaller grain and a semi-dwarf phenotype. The decreased grain size was caused by repressed cell expansion in spikelet hulls of the sg2 mutant. Using map-based cloning combined with a MutMap approach, we cloned SG2, which encodes a plant-specific protein with a ribonuclease H-like domain. SG2 is a positive regulator downstream of GLYCOGEN SYNTHASE KINASE2 (GSK2) in response to BR signaling, and its mutation causes insensitivity to exogenous BR treatment. Genetical and biochemical analysis showed that GSK2 interacts with and phosphorylates SG2. We further found that BRs enhance the accumulation of SG2 in the nucleus, and subcellular distribution of SG2 is regulated by GSK2 kinase activity. In addition, Oryza sativa OVATE family protein 19 (OsOFP19), a negative regulator of grain shape, interacts with SG2 and plays an antagonistic role with SG2 in controlling gene expression and grain size. Our results indicated that SG2 is a new component of GSK2-related BR signaling response and regulates grain size by interacting with OsOFP19.
粒型是决定植物产量的一个重要农艺性状。油菜素内酯（BRs）在水稻粒型调控中的作用已被广泛报道。然而，BR 信号通路与粒型的关系仍需要进一步研究。在这里，我们分离得到一个水稻突变体，命名为小粒 2 号（sg2），该突变体表现出粒小和半矮秆的表型。sg2 突变体的小粒表型是由于小穗颖壳细胞扩张受到抑制所致。通过图位克隆结合 MutMap 方法，我们克隆了 SG2，它编码一个具有核糖核酸酶 H 样结构域的植物特异性蛋白。SG2 是 GSK2 下游响应 BR 信号的正向调控因子，其突变导致对外源 BR 处理不敏感。遗传和生化分析表明，GSK2 与 SG2 相互作用并磷酸化 SG2。我们进一步发现 BRs 增强了 SG2 在核内的积累，并且 SG2 的亚细胞分布受 GSK2 激酶活性的调控。此外，水稻卵形蛋白 19（OsOFP19）作为粒型的负调控因子，与 SG2 相互作用，并在控制基因表达和粒型方面与 SG2 发挥拮抗作用。我们的结果表明，SG2 是 GSK2 相关 BR 信号响应的一个新组成部分，通过与 OsOFP19 相互作用来调节粒型。
